Bending Rolls

[BaldricParticipant @baldric]

I have a few jobs to do on my 3″ Foden build, that will require bending some sheet material. I have been looking at the GH Thomas design, as designed they are not wide enough, I need 12″. Are there any other plans for similar rolls? I could just make them bigger, but not sure on the diameter of rolls that I would require to cope with the extra length & thickness.

Requirements are

Copper, 3.25mm x 300mm, OD 6 1/4″

Steel, 1.22mm x 235mm, ID 1 7/8″

Rather than roll the copper, I guess I could create a wooden former to create a tube, but will the original design cope with the steel that size?

Thanks,

Mark

[Andrew CrowParticipant @andrewcrow91475]

Hi Mark, you could upscale the GHT design by say 25% which would give you a width of about 312mm, the actual size of the rollers would depend on the centres of the gears that you use. The 20dp gears used in the original design should be OK if you make them from something like EN8 but obviously would need more teeth to accommodate larger diameter rollers.

Andy

[Clive Brown 1Participant @clivebrown1]

I made my GHT rolls 12″ wide, rather than the 10″ as designed. No problem there. Mine don’t have gears as that suggested improvement hadn’t appeared then. However, I think that even the geared version might struggle with your work. The copper is on the thick side and the steel requires a tight radius. Only my guess though.

[Roderick JenkinsParticipant @roderickjenkins93242]

Mark,

When I made mine I used 30mm x 330mm silver steel from Cromwell/Zoro.  I drilled the ends and inserted the bearing ends, retained with Loctite.  I used the gears as specified by GHT, making my own from FC steel and they are perfectly satisfactory.

I’m not sure whether they would roll copper that thick, even if well annealed.

HTH,

Rod

[bernard towersParticipant @bernardtowers37738]

Made mine from 50cc motor cycle fork stanchions  and are about 15″ long with  extended end shafts with keys so you can fit short rolls with grooves/shapes etc.

[noel shelleyParticipant @noelshelley55608]

I doubt that whats been mentioned will do the copper and may well struggle with the steel at that radius. Far it out to a company with the proper gear may be best. If your near me I have a set you could use, or try .  Noel.

[john fletcher 1Participant @johnfletcher1]

I followed GHT details, but made the rollers 410 mm wide, using ex car suspension unit chromed rods. Cut the gears using my Arduino controller rotary table. Thanks to Carl Wilson  article in MEW number 249. Not used very often but works well.  John

[Howard LewisParticipant @howardlewis46836]

My bending rolls are 12″, merely an extended version of the GHT design.

You may struggle with 3.25 mm copper.

But try it, in SMALL increments, with the copper being annealed frequently.

Good Luck!

Howard

[Dave HalfordParticipant @davehalford22513]

Small increments work with 3mm steel 3″ wide rolled to 6″ dia, the gears won’t mesh but the rolls drive anyway.

Thickness limits on rolls are based on full width work.

You may get away the with copper at that width by a lot of annealing.

Your steel would be equivalent to 3.66mm thick 3″ wide and very hard work to get down to 1.7/8″.

[BaldricParticipant @baldric]

Thanks for the comments, I have been looking, but not replying as viewing on my phone, I don’t find it convenient to use that to reply with.

Dave Halford’s comment on the gears not meshing with 3mm steel is an interesting one, as I though the design allowed for that to a certain extent, with 4 gears, the top set may be slightly out of perfect mesh, but not that far out. I will look at that, perhaps with bigger teeth gears. I have also thought that I could use a smaller gear driving the 4, rather than a longer handle, to drive it all, this may make it easier to use, but does not negate any limit reached because of the roll diameter.

Overall, as there does not appear to be a formula that says it won’t work or will, just I may/will struggle, I will probably give it a go, on the grounds that I can use the parts to make a shorter set for the other sheet metal work required that is smaller & for some of the angle iron that will need forming. I will update as I progress.

Mark

[BaldricParticipant @baldric]

Just found that there is a set of plan by Martin Evans for rollers that sound like they will do what I wanted, Bending Rolls WE9 – Sarik Hobbies – for the Model Builder, described in MEW, December, 2013, has anyone got any experience of these rolls? I will do some investigation on these, including getting the relevant back issue, but that will probably not be until next weekend no.

Mark

[Engine BuilderParticipant @enginebuilder]

Mark, have a look at design WE59

I designed and built these years ago as a simple machine that will do the job but not be a long project for something that will only get occasional use.

They work well and I have even rolled 6mm x 30mm mild steel.

The design was published in Model Engineer, I can’t remember which issue but I do remember they condensed the drawings so small it did not take up many pages and so my payment was also condensed!

David

[Julie AnnParticipant @julieann]

For initial pinch rolls the work is a cantilever beam with a point load at the unsupported end. Using standard formulae it is straightforward to calculate the force needed to exceed the yield strength of the material at the bending point. That figure can then be used to estimate the size of the rollers needed to exert the force without unduly bending.

To avoid gears coming out of mesh simply use gears with a smaller DP. The gears in these home made bending rolls are 5DP:

The rolls were designed to accomodate 3/16″ x 3″ and 5mm x 150mm mild steel rectangular bar. When the gears are in full mesh the gap between the pinch rollers is 1/8″.

Julie

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, I also think you would struggle with 1″ x 12″ rolls, even with your steel, and especially if you are using pinch rolls. Engine Builder’s pyramid rolls (WE59) would be better, but you do get a straight bit at each end, which you would have to form first by hammering over the bottom rolls a bit at the time until you get a reasonable length of your radius at each end, and then turning it over to roll your tube, or start with a longer piece, roll it as far as you can, then cut off the straight pieces, and then reroll to close up. However, your top roll must be smaller the the I/D, which would probably mean it would have to be no bigger than about an inch & three quarters maximum in diameter.

Regards Nick.

[Howard LewisParticipant @howardlewis46836]

The usual advice (By G H T) on dealing with the straight bit at the start, is to run the work through the rolls again the other way round, so that the straight part is last to pass through the rolls.

Howard

[Baldric]

On Baldric Said:

Thanks for the comments, I have been looking, but not replying as viewing on my phone, I don’t find it convenient to use that to reply with.

Dave Halford’s comment on the gears not meshing with 3mm steel is an interesting one, as I though the design allowed for that to a certain extent, with 4 gears, the top set may be slightly out of perfect mesh, but not that far out. I will look at that, perhaps with bigger teeth gears. I have also thought that I could use a smaller gear driving the 4, rather than a longer handle, to drive it all, this may make it easier to use, but does not negate any limit reached because of the roll diameter.

Overall, as there does not appear to be a formula that says it won’t work or will, just I may/will struggle, I will probably give it a go, on the grounds that I can use the parts to make a shorter set for the other sheet metal work required that is smaller & for some of the angle iron that will need forming. I will update as I progress.

Mark

Sorry Mark,

To expand, my set is an Axminster 300mm 3in1 you get only 2 gears. My point was really it still works even when they don’t mesh and only using the existing tensioners tightened by hand

[BaldricParticipant @baldric]

I am trying to work out force required to bend the material, as per Julie’s suggestion, but failing to remember enough of my physics to put it in to practice.  I can understand that for initial pinch rolls, the bend is at the pinch rollers, with the “3rd” roller applying pressure to bend at the pinch roller, thus could calculate that from a simple formula.For the roller diameters, I am struggling, the material near the middle will apply more force to the rolls than that nearer the ends, leading me to think it is not a simple calculation. Am I over thinking this?

Mark

[Martin KyteParticipant @martinkyte99762]

The alternative to gearing the rolls together is attaching a second crank handle to the top roll on the left hand side.

[Baldric]

On Baldric Said:

I am trying to work out force required to bend the material, as per Julie’s suggestion, but failing to remember enough of my physics to put it in to practice.  I can understand that for initial pinch rolls, the bend is at the pinch rollers, with the “3rd” roller applying pressure to bend at the pinch roller, thus could calculate that from a simple formula.For the roller diameters, I am struggling, the material near the middle will apply more force to the rolls than that nearer the ends, leading me to think it is not a simple calculation. Am I over thinking this?

Mark

Having two sets of GHT’s Bending Rolls, the maximum pressure is applied at the edges of the sheet being rolled. This effect was shown in the pages of Model Engineer, but not in his book.

Exaggerated the Roll assumes the shape of an Archers bow, top and bottom, it is not so pronounced as the work gets wider.

Regards

Gray,

The smaller set is a scaled down set, but I have also built larger ones by doubling the dimensions, including the Roll diameter. The smaller set was for a friend who builds scratch built Locomotives in OO gauge.

You will always get straight portions with a Pyramid roll, see GHT’s Bending Rolls Fig 18.1 in his ME Workshop Manual.

Regards

Gray,

[noel shelleyParticipant @noelshelley55608]

I have a very neat set of slip rolls bit like the ones Graham has posted with 4 gears, made I think by Edwards. The rolls are 20″ wide and about 1.5″ dia. The top roll has a latch on one end and an interesting bearing on the other so it can be released to remove the work. It will do 4 or 5″ X 1/8″ (3mm) steel but thats the limit. Noel.

[Engine BuilderParticipant @enginebuilder]

I don’t find an issue with the flat section with my pyramid rolls.

Make the  stock over length and roll each end to the diameter needed with reference to a circle drawn on paper.

Then cut off the flat part and roll the rest of the metal.

An interesting thing with rolling is you cannot caluculate the length of metal needed using pi as it will stretch when rolled and come out too long.

This video shows my rolls and also my spindle raiser for maching large diameters in an ML10

https://youtu.be/m_-iPpEuWRA

David

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Engine Builder, to calculate the length of metal needed, you use the radius of the circle plus half the thickness of the metal, for the internal diameter, or minus half the metal thickness for the outside diameter, When you roll metal the outside stretches, and the inside is compressed, and the centreline of the metal will stay virtually the same length. Just add on enough metal for the straight bits at each end when using pyramid rolls, unless you form a long enough curve at each end first.

Regards Nick.

[Julie AnnParticipant @julieann]

When I did my calculations I treated the work as a cantilever to get an estimate of the force needed. I didn’t bother with calculating the roll diameter. I used 2-1/2″ diameter rolls, dictated mainly by the gears, as I already had a 5DP 12-13 tooth involute cutter.

I prefer initial pinch rolls. There is a flat on the starting end, but not on the finish end. So if the work is turned end for end at each pass you end up with a true circle and no flats. Makes the calculations easier and no waste of material.

For the wheel rims shown I calculated the length of metal needed using pi times diameter and assumed that the bend line would be in the middle of the thickness as the finished work diameter was fairly large. In other words compression and tension forces on the inner and outer edges would be equal and opposite.

The nominal OD was 14.5″; after rolling and welding the OD came out as ~14.48″. Good enough for me.

I keep telling myself I am not a perfectionist, but I do like things to be just so.

Julie

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